Multichannel telephone systems are found in many office and business settings. Such systems typically include a number of remotely located telephones that communicate through a key service unit with a primary communications link, such as external telephone lines or the like. In general, these individual telephones communicate with the key service unit through an electrical conductor such as copper wire.
These hard wired systems have certain benefits. For instance, the communications channels are not readily subject to interference or nonavailability due to interaction or proximity with other telephones. Further, by using solid conductors, many multichannel telephone systems can operate in close proximity to one another without incurring an unacceptable risk of interference between the systems.
Nevertheless, hard wired multichannel telephone systems also have many inherent problems. The installation of conductor paths can be costly and time consuming, and typically represents a permanent, or at least semi-permanent, installation. When users of such a system are moved about, and to the extent that operation layouts change, modifying the conductor paths also requires a substantial expenditure of time and money.
One proposed solution suggests the use of RF user channels; i.e., the telephones and the key service unit would communicate with one another via radio communications instead of solid conductors. Many benefits would result through use of such a system. For instance, the telephones could be initially located and subsequently moved virtually at will, so long as the telephones remained located within the transmission and reception ranges of the equipment.
Unfortunately, there are also many problems associated with such a system. For example, by one possible approach, the key service unit can have one RF transceiver for each allocated RF user channel. If a particular system had, for example, thirty-one different frequencies approved for use in the system, then the key service unit would have to have thirty-one transceivers as well. This represents an expense that reduces the feasibility of favorably comparing an RF based system to a hard wired one.
Another problem involves annoying delays that can be experienced between the time a user lifts the telephone handset and the time a dial tone is attained. These delays can arise because a communications link is attempted on a user channel that is not currently available (due to use of that channel by another telephone or due to interference). Also, delays can result because many users try to initiate a communications link substantially simultaneously. When this happens, many different telephones may try to simultaneously access the key service unit through the same user channel, thereby delaying the time until dial tones can be provided to all of the telephones.
With reference to yet another problem, interference can arise when two or more multichannel telephone systems using RF links are positioned within range of one another. Such interference also leads to delay and inefficiency.
With reference to yet still another problem, prior art systems tend to allow either the key service unit or the remote telephones to decide exclusively which channel a communications link will be attempted on. This can lead to problems in a dispersed system where a given channel may appear available in one location and yet not be available in another location due to local interference. If, for instance, the key service unit exclusively makes all decisions regarding channel usage, then a channel it selects may in fact not be available to the telephone, even though it might appear available to the key service unit. This can lead to significant disruption of service.
There therefore exists a need for a multichannel telephone system that can minimize the expense of key service unit transceiver needs while simultaneously allowing RF links to be utilized, that can minimize delay time in obtaining a dial tone, and that can minimize problems associated with adjacent systems.